For a transmitter of radio communication, a power amplifier is used to transmit radio waves in air. The power amplifier needs to output a signal of large power and is thus a block consuming large power in the transmitter. Therefore, it is important to increase the power efficiency of the power amplifier to decrease the power consumption.
There is a known amplifier circuit which includes a function of applying a power supply voltage modulated based on an input signal to an amplifier to the amplifier, a function of estimating an inverse distortion characteristic on the basis of input/output characteristics of the amplifier and performing distortion compensation, and a function of adjusting mutual timings of the input signal and the power supply voltage applied to the amplifier, in which in a state that the distortion compensation by a distortion compensating unit is not performed, an output of the amplifier is increased by timing adjustment from an output whose timing has not been adjusted at the time when an adjustment signal having a peaked waveform is inputted into the amplifier so as to cause a peak value to appear, and timing adjustment is performed so that a value corresponding to the width (gain width or the like) of the input/output characteristics at an output near the peak value and lower than the peak value becomes a predetermined value (ideally, 0) (refer to, for example, Patent Document 1).
There also is a known amplifier circuit which includes an amplifier, a power supply modulation circuit that applies a power supply voltage modulated based on an input signal to the amplifier, and a distortion compensation circuit that is placed ahead of the amplifier and generates an inverse distortion characteristic cancelling a distortion characteristic of the amplifier and adds the inverse distortion characteristic to the input signal, in which a gain adjusting circuit is provided between the distortion compensation circuit and the amplifier, and an inverse characteristic shaping a frequency characteristic of the amplifier irrespective of the power supply voltage is a frequency characteristic of the gain adjusting circuit (refer to, for example, Patent Document 2).
Further, there is a distortion compensation amplifier which includes an amplifier circuit that may include a distortion component in an amplified output signal, a first detection means that detects the amplitude of an input signal, a second detection manes that detects the amplitude of the output signal, and an amplitude control means that is inserted and connected to the previous stage of the amplifier circuit and controls the amplitude of a signal introduced into the amplifier circuit so that the difference or ratio between the amplitudes detected by the first detection means and the second detection means converges (refer to, for example, Patent Document 3).
Patent Document 1: Japanese Laid-open Patent Publication No. 2009-232296
Patent Document 2: Japanese Laid-open Patent Publication No. 2011-211533
Patent Document 3: Japanese Laid-open Patent Publication No. 2002-353744